1. Technical Field of the Invention
The present invention relates to a turbofan engine which has a high bypass ratio and can achieve a favorable mileage and a low noise.
2. Description of Related Art
FIG. 1 is a schematic block diagram of an aircraft engine 51 (a turbojet engine). As shown in this drawing, the turbojet engine is provided with a fan 52 taking an air therein, a compressor 53 compressing the intake air, a combustor 54 burning a fuel by the compressed air, a turbine 55 driving the fan 52 and the compressor 53 by a combustion gas of the combustor 54, an after burner 56 afterburning for increasing a thrust and the like.
The after burner 56 comprises a flame holder 57 having a triangular cross section or the like and forming a circulating region in a downstream side so as to hold the flame, a fuel nozzle 58 for jetting the fuel, a spark plug 59 and the like, and is structured such as to jet from an exhaust nozzle 62 through an inner side of a liner 61 inside an after duct 60, thereby increasing the thrust.
The turbojet engine in which the fan 52 taking the air therein is enlarged in size and a bypass ratio is enlarged is called as “turbofan engine”. The bypass ratio corresponds to a flow rate ratio (bypass flow/core flow) between an air flow (a core flow) flowing into a core engine (the compressor 53, the combustor 54 and the turbine 55 mentioned above) and a bypass flow bypassing them. There is obtained an effect of reducing a flow speed of an exhaust jet and lowering a noise and a specific fuel consumption, in accordance with an increase of the ratio. In this case, a prior art relating to the jet engine is disclosed, for example, in the following patent documents 1 and 2 corresponding to Japanese Unexamined Patent Publications.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 8-189419
[Patent Document 2]
Japanese Unexamined Patent Publication No. 11-22486
However, in the turbofan engine mentioned above, there is a problem that a fan first-stage moving blade (an up-front fan) and an inner diameter of a casing surrounding the fan first-stage moving blade are enlarged by enlarging the bypass ratio, and a weight of the engine is increased.
In other words, since a fan first-stage moving blade 52a structured such as to be embedded into a spinner 63 of the turbofan engine has an embedded structure, a certain degree of hub/chip ratio (inlet hub diameter/inlet chip diameter) is necessary, and an area of the fan inlet is narrowed at a degree of an area of the spinner.
Therefore, if it is intended to increase the bypass ratio for achieving the favorable mileage and the low noise, it is necessary to further widen the diameter of the fan and the inner diameter of the casing, so that the weight of the engine is increased.